1. Field of the Invention
The invention relates to an improved system for generating electrical power using a fuel cell. More particularly, the invention pertains to a system for generating hydrogen gas by reacting water vapor with a substantially non-fluid substance in a regulated manner, and transporting the generated hydrogen gas to the fuel cell which in turn generates electrical power. The invention also relates to a pneumatic valve for use in a hydrogen gas generating apparatus.
2. Description of the Related Art
Similar to batteries, fuel cells function to produce electric power through chemical reactions. Rather than storing reactants as batteries do, fuel cells are operated by continuously supplying reactants to the cell. Proton exchange membrane (PEM) fuel cells operating with H2 from hydrocarbon liquids have emerged as leading candidates to replace batteries in portable electronic devices, power cleaners, more fuel efficient vehicles and for powering microelectromechanical systems (MEMS) devices such as MEMS electrical power generators. In a typical fuel cell, hydrogen gas acts as one reactant and oxygen as the other, with the two reacting at electrodes to form water molecules and releasing energy in the form of direct current electricity. This direct current electricity may then be converted into an alternating current. The system may produce electricity continuously as long as hydrogen and oxygen are provided. While oxygen is typically provided from the air, it is generally necessary to generate hydrogen gas from other compounds through controlled chemical reactions rather than storing hydrogen, because storing of hydrogen gas requires that it either be compressed or cryogenically cooled. As fuel cell technology evolves, so do the means by which hydrogen gas is generated for application with fuel cells.
Currently, there are various methods which are known and employed for generating hydrogen gas. The predominant method is by a process known as reformation in which fossil fuels are broken down into their hydrogen and carbon products. However, this system is undesirable in the long term because it is dependent upon a non-renewable resource. Another method is electrolysis, in which hydrogen is split from water molecules. However, this method is not well suited for large scale applications, such as use in automobiles. Another means of generating hydrogen gas is by reversibly adsorbing and releasing hydrogen gas from metal hydrides or alloys through heating. While this method is useful, it is not preferred because the metal hydrides are typically very heavy, expensive and only release small quantities of hydrogen. Yet another means by which hydrogen gas is generated is through reactive chemical hydrides. This process involves chemically generating hydrogen gas from dry, highly reactive solids by reacting them with liquid water or acids. Chemicals especially suitable for this process are lithium hydride, calcium hydride, B10H14, lithium aluminum hydride and sodium borohydride, each of which are capable of releasing plentiful quantities of hydrogen. The disadvantages associated with this method is that reaction products from the chemical and liquid water typically form a cake or pasty substance which interferes with further reaction of the reactive chemical with the liquid water or acid.
It is of great interest in the art to provide a means by which hydrogen gas may be generated in a regulated manner for use in fuel cells, without relying on non-renewable resources and without the disadvantages of each of the aforementioned methods. The present invention provides a solution to this problem. The invention provides an electrical power generator and a process for controllably generating hydrogen gas at the rate that a fuel cell requires it. The electrical power generator comprises a water vapor generator at least partially filled with water vapor, at least one hydrogen gas generator connected to the water vapor generator, a regulating valve and a fuel cell connected to the hydrogen gas generator, the hydrogen generation chamber being at least partially filled with a substantially non-fluid substance which reacts with water vapor to generate hydrogen gas. The hydrogen gas generated may then be used as a “fuel” which allows the fuel cell to generate electrical power. The present invention improves upon the related art by reacting a water vapor with a substantially non-fluid substance to controllably generate hydrogen gas, rather than liquid water. By reacting a water vapor with the aforementioned non-fluid chemical substance, it has been found that the typical problems associated with reactive chemical hydrides are avoided, resulting in a more efficient system than those of the prior art.
The invention also provides a non-electrically actuated valve suitable for use in hydrogen generating apparatuses. The valve of the invention is actuated by hydrogen overpressure to regulate the diffusion of water vapor into a powdered chemical fuel. Since the valve is non-electrically actuated, the need for a control voltage, a controller and a control voltage generator is eliminated, and the problem of electrical discharge in valves operating in humid conditions is avoided.